scholarly journals Identification of dynamical characteristics for distributed parameters systems from measured vibration data

1995 ◽  
Vol 17 (1) ◽  
pp. 35-44
Author(s):  
Nguyen Tien Khiem ◽  
Dao Nhu Mai ◽  
Nguyen Van Dac ◽  
Nguyen Viet Khoa
Keyword(s):  
Natural Frequencies ◽  
Damping Ratio ◽  
Elastic Beam ◽  
Mode Shapes ◽  
Vibration Data ◽  
Dynamical Characteristics ◽  
Distributed Parameters

This article is devoted to determinate the dynamical characteristics (Natural Frequencies, Mode Shapes, Damping Ratio) of elastic beam from measured responce auto-spectrum. Developed here method is based on the assumptions of smallness of the damping and sparse distribution of natural frequencies. Accuracy and practical meaning of the method are confirmed by the agreement of the theory with experiments.

Extending Blind Modal Identification to the Underdetermined Case for Ambient Vibration

2012 ◽  
Author(s):  
Scot McNeill
Keyword(s):  
Natural Frequencies ◽  
Second Order ◽  
Modal Identification ◽  
Ambient Vibration ◽  
Mode Shapes ◽  
Frequency Domain Method ◽  
Blind Identification ◽  
Vibration Data ◽  
Modal Damping ◽  
Six Dof

The modal identification framework known as Blind Modal Identification (BMID) has recently been developed, drawing on techniques from Blind Source Separation (BSS). Therein, a BSS algorithm known as Second Order Blind Identification (SOBI) was adapted to solve the Modal IDentification (MID) problem. One of the drawbacks of the technique is that the number of modes identified must be less than the number of sensors used to measure the vibration of the equipment or structure. In this paper, an extension of the BMID method is presented for the underdetermined case, where the number of sensors is less than the number of modes to be identified. The analytic signal formed from measured vibration data is formed and the Second Order Blind Identification of Underdetermined Mixtures (SOBIUM) algorithm is applied to estimate the complex-valued modes and modal response autocorrelation functions. The natural frequencies and modal damping ratios are then estimated from the corresponding modal auto spectral density functions using a simple Single Degree Of Freedom (SDOF), frequency-domain method. Theoretical limitations on the number of modes identified given the number of sensors are provided. The method is demonstrated using a simulated six DOF mass-spring-dashpot system excited by white noise, where displacement at four of the six DOF is measured. All six modes are successfully identified using data from only four sensors. The method is also applied to a more realistic simulation of ambient building vibration. Seven modes in the bandwidth of interest are successfully identified using acceleration data from only five DOF. In both examples, the identified modal parameters (natural frequencies, mode shapes, modal damping ratios) are compared to the analytical parameters and are demonstrated to be of good quality.

Dynamic and Vibration Analysis of a SAR Membrane Antenna

2007 ◽  
Author(s):  
Yu Shen ◽  
Wanping Zheng ◽  
Xiaoyun Wang
Keyword(s):  
Attitude Control ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Mode Shapes ◽  
Base Excitation ◽  
Control Torque ◽  
Satellite Attitude ◽  
Satellite Attitude Control ◽  
Low Mass

Synthetic Aperture Radar (SAR) membrane antennas have attracted much attention for their low mass, small stowed volume, large gain and high resolution. To deploy a membrane antenna requires a deployable support structure providing deployment and rigid support after it is fully deployed. A membrane antenna’s vibration may be caused by the disturbance of the satellite attitude-control torque in spacecraft, and it is determined by the mechanical properties of the membrane and its in-plane tension loads. In this paper, the dynamic properties of the deployable structure are studied with ADAMS when the flexibility of the frames is considered. The mode shapes and the natural frequencies of the membrane are analyzed with ABAQUS when the pre-tension loads provided by the tension cable are changed. The random response of the membrane subjected to the base excitation is studied for different tension forces and damping ratios. This work provides a guideline for the vibration control of the membrane by controlling its tension force or damping ratio.

Modal Testing and Finite Element Calculations for Lightweight Aluminum Panels in Car Carriers

2006 ◽  
Vol 43 (01) ◽  
pp. 11-21
Author(s):  
Junbo Jia ◽  
Anders Ulfvarson
Keyword(s):  
Finite Element ◽  
Natural Frequencies ◽  
Damping Ratio ◽  
Element Model ◽  
Modal Testing ◽  
Structural Behavior ◽  
Mode Shapes ◽  
Maintenance Cost ◽  
Car Suspension ◽  
Aluminum Panels

Due to their characteristics and lower maintenance cost, lightweight aluminum structures have been widely used for manufacturing deck structures. When this type of structure is developed, the natural frequencies for the unloaded deck may increase, while the natural frequencies for loaded decks are most likely to decrease and new problems of vibration and damping may appear. In addition, it has already been shown by the authors that compared to the load effects of normal cargo, the dynamic structural behavior of a vehicle-loaded deck is different due to the participation of vehicle vibrations. The current paper presents a modal analysis by both testing and finite element (FE) calculation for a lightweight deck using aluminum panels. By comparing the results between the unloaded and car-loaded cases, it is shown how vehicle loading influences the dynamic structural behavior of the deck structures. The authors report that an aluminum panel mechanically connected to a steel frame may participate in some mode shapes of vibrations that significantly increase the corresponding damping ratio. The reasonably good agreement between modal testing results and FE calculations validates the finite element model, which may then be used for further dynamic analysis. The authors found that the spring-damping systems of car suspension and tires can interfere in the dynamic transmission of the vehicle mass into the deck structure. The study enables structural engineers interested in the design of car carriers to have a better understanding of how the vehicles parked on decks can influence the dynamic characteristics of the vehicle deck systems.

An Investigation of the Temperature Influence on a Shift of Natural Frequencies Using Digital Image Correlation

2014 ◽  
Vol 611 ◽  
pp. 506-510 ◽  
Author(s):  
Martin Hagara ◽  
Martin Schrötter ◽  
Pavol Lengvarský
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
High Speed ◽  
Natural Frequencies ◽  
Damping Ratio ◽  
Indicator Function ◽  
Image Correlation ◽  
Mode Shapes ◽  
Temperature Influence ◽  
Air Gun

The contribution describes an original optical measuring technique serving for the investigation of temperature influence on the shift of investigated objects natural frequencies. The mentioned method uses a modified high-speed digital image correlation system with original program Modan 3D created in Matlab, by which it is possible to non-contactly determine the natural frequencies using complex mode indicator function (CMIF) or normal mode indicator function (NMIF), the mode shapes as well as the damping ratio. Influence of the temperature on the shift of natural frequencies was analyzed at the planar steel specimen of circular shape with three holes. To the excitation a modal hammer was used. The specimen heating was realized by a hot-air gun, whereby the influence of the elevated temperature on the shift of natural frequencies was investigated by three temperatures distinguishing the room temperature 50° C, 75° C and 100° C.

Vibration-Based Damage Detection in Structural Members Utilizing Finite Elements and Evolutionary Algorithms

2006 ◽  
Author(s):  
Amir Poursamad
Keyword(s):  
Finite Elements ◽  
Damage Detection ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Fe Model ◽  
Structural Members ◽  
Vibration Data ◽  
Detection Approach ◽  
The Difference ◽  
Extent Of Damage

Presented within this paper is the application of finite elements method combined with an evolutionary algorithm to the problem of damage detection in structural members using vibration data. The objective is to identify the position of the damage in structure, and to estimate the extent of the damage. To describe the damage, finite element method (FEM) is used here and the damage is modeled as a reduction in the stiffness of the associated element. Using this model, the effect of damage on the vibration characteristics of the structure is studied. The problem of damage detection is then formulated as an optimization problem. The decision variables are the position of damaged element and the extent of damage. The objective function is considered as the difference between measured natural frequencies and those obtained from FE model of the structure. Only natural frequencies are adopted here, because the measurement of mode shapes is usually accompanied by larger amount of error. The proposed damage detection approach is verified and assessed using a simulated cantilever Euler-Bernoulli beam.

An Analytical Investigation for Vibration Characteristics of a Beam-Type Liquid Micro-Pump

2020 ◽  
Vol 12 (02) ◽  
pp. 2050016
Author(s):  
Hamed Hatami ◽  
Ahmad Bagheri ◽  
Reza Ansari
Keyword(s):  
Fluid Flow ◽  
Natural Frequencies ◽  
Separation Of Variables ◽  
Elastic Beam ◽  
Coupled System ◽  
Analytical Investigation ◽  
Mode Shapes ◽  
Micro Pump ◽  
Cartesian Coordinate ◽  
Forced Vibration Analysis

This paper studies the characteristics of a micro-beam interacting with an incompressible fluid in a fluid chamber with an opening in its bottom face for fluid flow. The Euler–Bernoulli equation for transverse deformation of an elastic beam is coupled with the fundamental hydrodynamic equation, which is solved by Galerkin and separation of variables method. The 2D fluid flow assumption in Cartesian coordinate has been used. Natural frequencies and mode shapes of wet beam are calculated and compared with the dry beam. The effects of geometrical parameter changes are also computed as a benchmark for the design of the micro-pump. It is observed that fluid coupling causes a decrease for beam’s natural frequencies, especially in higher modes. Furthermore, since the results of the dry and wet beam show a small discrepancy in lower modes, the mode related to the dry beam was employed as the trial function in the forced vibration analysis of the coupled system.

scholarly journals Building monitoring in Bishkek and Dushanbe by the use of ambient vibration analysis

2015 ◽  
Vol 58 (1) ◽  
Author(s):  
Bojana Petrovic ◽  
Dino Bindi ◽  
Marco Pilz ◽  
Matteo Serio ◽  
Sagynbek Orunbaev ◽  
...  
Keyword(s):  
Natural Frequencies ◽  
Residential Building ◽  
Short Description ◽  
Ambient Vibration ◽  
Mode Shapes ◽  
Dynamical Characteristics ◽  
Building Monitoring ◽  
Earthquake Model ◽  
Set Up ◽  
Frequency Domain Decomposition

<p>Within the framework of the EMCA - Earthquake Model Central Asia - project, the cities of Bishkek (Kyrgyzstan) and Dushanbe (Tajikistan) were selected for building monitoring using measurements of seismic noise to obtain the dynamical properties of the buildings. Eight buildings of different construction types, date of construction and building height, both, Soviet-era and recently constructed buildings, were instrumented for a period of a few hours. In this study, an overview of the experiment is given, including a short description of each monitored building’s structure and the performed installation. Preliminary results for a representative Soviet-era residential building in Dushanbe are presented. Modal analysis is performed using the Frequency Domain Decomposition (FDD) method to estimate the natural frequencies and the mode shapes. The wave propagation velocities in the two directions along the building axes are determined by an interferometric approach. Although the experimental set-up was not the optimal, valuable information about the dynamical characteristics of the buildings were still obtained.</p>

scholarly journals Somes problems in the identification of elastic beam by the dynamical characteristics

1995 ◽  
Vol 17 (3) ◽  
pp. 20-26
Author(s):  
Nguyen Tien Khiem
Keyword(s):  
Boundary Condition ◽  
Mechanical System ◽  
Unique Solution ◽  
Analytical Method ◽  
Natural Frequencies ◽  
Elastic Beam ◽  
Dynamical Characteristics

Two problems in the identification of Mechanical system are presented and solved by the analytical method. Firstly, the length of an elastic beam is found from measured natural frequencies. Secondly, the boundary condition of the beam was also obtained with given frequencies. In both the cases, unique solution can be found only with condition, that is given in this paper.

Experimental and numerical investigation on dynamic parameters of broaching machine

2015 ◽  
Vol 231 (10) ◽  
pp. 1907-1920
Author(s):  
Shenshun Ying ◽  
Shiming Ji ◽  
Yangyu Wang ◽  
Zhixin Li ◽  
Lvgao Lin ◽  
...  
Keyword(s):  
Modal Analysis ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Structural Parameters ◽  
Damping Ratio ◽  
Experimental Results ◽  
Mode Shapes ◽  
Fe Model ◽  
Dynamic Parameters ◽  
Machine Structure

Dynamic properties of the whole broaching machine structure greatly contribute to the broaching quality and efficiency. However, it is hard to measure the dynamic parameters because they will change during operation compared with the static results from classic experimental modal analysis. This study is to examine the dynamic parameters of broaching machine LG7120KT using both the numerical finite element (FE) method and the experimental operational modal analysis (OMA). Firstly, FE analysis model of the broaching machine with the real dimension is constructed and calculated. Second, experimental results are obtained from OMA in practical broaching process, which can be used to identify steady-state modes. Modal parameters including mode shapes, damping ratio, and natural frequencies are examined, using both LMS SCADAS III-305 system and PolyMAX method in OMA. The numerical and experimental results show high agreement in their calculated natural frequencies. From the modal analysis results, it is also found the vibration normal to cutting direction can be greatly reduced by adjusting broaching speed. From the topology optimization result based on the already correlated FE model, we redesigned a lightweight machine structure with a better dynamic performance, due to its lower displacement of broaching machine at force point and its higher first-order natural frequency. The experimental and numerical results in this paper help to design the structural parameters of broaching machine and propose a better broaching process.

The Effect of Close or Repeated Eigenvalues on the Updating of Model Parameters from FRF Data

1992 ◽  
Vol 114 (4) ◽  
pp. 514-520 ◽  
Author(s):  
M. I. Friswell ◽  
J. E. T. Penny
Keyword(s):  
Natural Frequencies ◽  
Analytical Models ◽  
Mode Shapes ◽  
Model Parameters ◽  
Finite Element Models ◽  
Reduced Order ◽  
Vibration Data ◽  
Modal Model ◽  
Equation Error ◽  
Error Method

Methods to update the parameters of finite element models using measured vibration data usually use the experimentally derived modal model, that is, the system natural frequencies, damping coefficients, and mode shapes. Alternatively the frequency response functions have been used directly to update condensed analytical models and so avoid the sometimes difficult step of deriving the modal model. Previously the authors suggested an algorithm using FRF data that is basically a weighted equation error method based on a reduced order model. This paper investigates the performance of the algorithm for systems with closely coupled or repeated natural frequencies or eigenvalues.

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